The oil on California beaches (tar balls) came from natural sepage. The drilling done from the platforms in the Santa Barbara Channel, Long Beach harbor, and Seal Beach reduced the gas pressure and drasticly cut the hugh daily flow of oil into the ocean.
Before there was any drilling or shipping (in the 1940s) the first stop returning from the beach when I visited my grandparents in Del Mar was the tin wash tub outside where I got a scrub down with a scrub brush and kerosene to remove all the tar.
Before the drilling in Long Beach and Seal Beach, There was thousands of barrels of oil a day boiling up on the Horseshoe Kelp (7 miles off Los Angeles harbor), some balls as big as basketballs that made an oil slick all the way to Mexico and tarred all the beaches on the way.
Golita, north of Santa Barbara, was so covered with tar that you couldn't use the beach (the Spanish used to beach there ships there to tar the bottoms) and since the drilling in the channel has reduced the natural flow, the beaches are clean and usable.
The only reason not to drill for oil off our coast is for the environmentalist to use it as an excuse to squeze us into an immobile and totally controled society, long one of the tennants of the communists.
Cheap abundants energy creates a mobile and affluent society which is at cross purposes of our government and the left.